| Vortex street flow meter, Known as Karman's whirlpool flow meter, which has advantages of simple structure, high reliability, long life and wide measuring scope etc. Therefore, it applies widely. According to the requirement of Measuring Appliance Research Institute in Hebei Hongye Machinery Co., this dissertation demonstrates "low power intelligent vortex street flow meter system".This system mainly includes the vortex sensor signal conditioning circuit and the low power digital signal processing circuit. The vortex sensor is made of the piezoelectricity ceramics, which can induce the vortex street lateral thrust. It is able to produce alternating electric charge signal that is proportional to vortex frequency. The vortex sensor signal conditioning circuit is composed of the electric charge amplifier, the alternating-current amplifier, second order active low-pass filter and the Schmitt shaper, which transforms the alternating electric charge signal into the pulse frequency signal, that can be captured by MCU. The traditional circuit has poor discharge coefficient linearity when measuring lower-limit frequency and is hard to measure the nominal upper limit frequency. We did a lot of experiments and made qualitative and the quantitative analysis on the existing problems, readjusted the circuit structure and resistance and capacitance parameters. Now the new circuit not only can measure accurately low flow, but has much more wider pass band. Moreover, by selecting amplifier's coefficients and resistance-capacitor parameters with multiplexer, the circuit realized the automatic gain control function and can be used in any pipes with different diameter and different fluid medium such as liquid, gas, saturation steam etc.The intelligent vortex flow meter makes use of newly ultra low-power mixed-signal microcontroller MSP430F149 which has powerful process faculty and abundant modules, as its intelligent measuring, transferring and processing unit. It works out instantaneous delivery and cumulative flux and displays both by LCD. Simultaneously it can measure temperature and realize the mass measurement of saturated steam by temperature compensating. It uses five sections of linear interpolation method to revise appliance flow coefficient, thus, the measuring accuracy increased greatly. The system outside expanded nonvolatile ferroelectric random memory as storage medium for significant information such as cumulative flux, it is preserved when interval time expired or system is power down. The circuit adopts double power source supply, the system can be powered by either battery or external power supply, and switchs automatically. Real-time monitoring battery voltage, low power alarm and power-down protection make system have higher reliability. The key design is man-machine interactive interface. The user can not only set float parameters like liquid density, sampling time, flow upper limit,flow lower limit, instrument parameter, compensates method etc, but also can clear cumulative flux by password. That MCU is applied in processing and calculating vortex flow signal makes system more intellectualized.Hardware circuit and system software both are adopting low power design concept, making CPU keep sleep as long as possible. The periphery chips all are low voltage, micro power and can be switch off by MCU. The quiescent power dissipation of final system is lower than 256μA; the dynamic peak power dissipation is below 600μA. A 3.6V/5.4AH lithium battery may guarantee the system works reliably above for 2.5 years.Massive experiments show that the low power intelligent vortex flow meter runs reliably, work stably, measures correctly, operates conveniently, system data are safety and anti-jamming capability is well. It achieved Technical specification of manufactory.
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